1. Field of the Invention
The present invention relates to a hollow or solid rod member which is subject to oscillation and which is a member of a vibration transmitting system such as shafts, arms, or conduits used in various devices, and more particularly to such an oscillating rod member which is equipped with a dynamic damper for restraining or absorbing vibrations of the oscillating rod member.
2. Discussion of the Related Art
Various kinds of rod members such as shafts or arms functioning as power transmitting members and such as conduit or pipes serving as a fluid passage generally tend to oscillate or vibrate and consequently resonate due to an external oscillating force. Further, the rod member undesirably transmits a vibration excited therein to other components of a device in which the rod member is used. As a method to cope with these problems, a dynamic damper is attached to the rod member for preventing the resonance of the rod member and the transmission of the excited vibration of the rod member to the other components.
There have been proposed various types of such dynamic dampers adapted to be installed on the oscillating rod member as described above so as to exhibit effective damping characteristics with respect to a bending vibration and a torsional vibration of the rod member. Examples of such a dynamic damper for use with a drive shaft of a motor vehicle are disclosed in U.S. Pat. No. 5,056,763 assigned to the assignee of the present application and laid-open Publication No. 2-190641 of unexamined Japanese Patent Application, wherein the dynamic damper has a mass member having a generally cylindrical configuration and elastic support members formed on axially opposite sides of the mass member. The disclosed dynamic damper is inserted onto a vehicle drive shaft as an oscillating rod member and secured thereto at the elastic support members.
In the thus constructed dynamic damper, an inside diameter of the elastic support members is suitably determined according to an outside diameter of the oscillating rod member on which the dynamic damper is installed, so that the inner circumferential surfaces of the elastic support members are fixed in close contact with the corresponding outer circumferential surfaces of the rod member. Further, in order to permit the dynamic damper to exhibit effective damping characteristics with respect to the vibration of the rod member, the resonance frequency of the dynamic damper is properly tuned so as to damp or absorb the input vibration received from the rod member, by suitably adjusting the mass of the mass member and the spring constant of the elastic support members.
However, the oscillating rod member is required to have a sufficiently high mechanical strength and excellent durability while making it possible to reduce the overall weight thereof and to lower the manufacturing cost. In view of these requirements, the oscillating rod member is often subject to alterations in dimensions such as the outside diameter so as to meet a slight change in the specifications of the device in which the rod member is used. In this case, the oscillating rod members do not have the same dimensions even if the rod members are employed in the same type of the device. The slight alterations in the dimensions or design of the rod members undesirably change the resonance frequencies of the associated components, and consequently change the frequency of vibration of the rod member to be damped. Thus, it has been quite difficult to use the same dynamic dampers for the rod members whose dimensions slightly differ from each other. Accordingly, it has been required to design and produce a specific dynamic damper for each of the different rod members.
Described more specifically, a drive shaft for a motor vehicle adapted to transmit a driving torque from a final speed reduction gear unit to driving wheels is usually equipped with a dynamic damper for damping the vibration of the drive shaft which arises from a variation in the rotating torque received from the final gear unit, to minimize such vibration that adversely influences ride comfort of the motor vehicle and durability of the components which are subject to the vibration. However, the drive shafts generally have different values of the outside diameter and oscillating frequency to be damped, depending upon models of the motor vehicles, more specifically, depending upon the engine output characteristics of the vehicles, for instance. Therefore, the dimensions of the dynamic damper are conventionally designed such that the mass of the mass member and the spring constant of the elastic support members of the dynamic damper are tuned or adjusted to the individual drive shafts, depending upon the outside diameter and oscillation frequency of the drive shaft on which the dynamic damper is installed.
Thus, the conventional oscillating rod members require respective dynamic dampers specifically adapted thereto, leading to increased costs of design and manufacture of the rod members equipped with the dynamic dampers.